1. Field of the Invention
The invention relates to a signal processing apparatus and, more particularly, to an apparatus for digitally modulating input data and outputting the modulated data.
2. Related Background Art
As such a kind of apparatus, hitherto, there has been known, for example, a digital VTR for recording and reproducing a digital signal to/from a recording medium.
In such a digital VTR, particularly, in a digital VTR for industrial use, when a digital signal is recorded to a magnetic tape, it is necessary to raise a recording density by narrowing a track width as much as possible or the like and thereby to reduce a consumption amount of the magnetic tape. As a result, the recording track width is narrowed as mentioned above, and in order to correctly reproduce a recording signal, what is called a tracking for allowing a head to accurately trace the recording track is important.
An apparatus for multiplexing a pilot signal to a recording signal for tracking in a digital VTR to a recording signal is disclosed in Japanese Patent Application Laid-Open No. 4-255969.
FIG. 1 is a block diagram showing a conventional construction of such a kind of apparatus for multiplexing the pilot signal to the recording signal.
In FIG. 1, a recording signal subjected to predetermined processes is inputted from an input terminal 1 and a code "1" or "0" is added to recording data of (n) bits by a modulation circuit 2, thereby converting to two kinds of data of (n+1) bits. Those two kinds of modulation data are respectively outputted to correlation detection circuits 4 and 7. A correlation between each modulation data and a pilot signal to be multiplexed having a predetermined frequency (f) is detected. Signals according to such correlations are respectively outputted to a selection circuit 11.
Specifically speaking, in the correlation detection circuit 4, a sine wave signal (hereinafter, "sine" is simply referred to as a "sin") from a sin wave signal generation circuit 61 and a cosine wave signal (hereinafter, "cosine" is also simply referred to as a "cos") from a cos wave signal generation circuit 51 are respectively multiplied by the inputted recording data and results of the multiplications are added, thereby detecting a correlation. Components in the case where the pilot signal of the frequency (f) is separated to a sin component and a cos component are respectively outputted as multivalues from the sin wave signal generation circuit 61 and cos wave signal generation circuit 51.
The selection circuit 11 controls a switch 3 so as to select the modulation data having a higher correlation on the basis of a signal indicative of the correlation outputted from each correlation detection circuit.
By modulating the recording data as mentioned above, the pilot signal component of the frequency (f) is multiplexed.
In the conventional apparatus as mentioned above, however, when the correlation between each modulation data and the pilot signal is detected, the multiplications of the multivalues of the sin wave and cos wave are executed, so that there is a drawback such that multipliers and adders of large digit numbers are necessary and a circuit scale increases.
There is also a drawback such that a data amount of the correlation values obtained and a scale of a circuit to compare the correlation values is large.